Grain oriented electrical steel sheets mainly used as iron cores of transformers are required to have excellent magnetic properties, in particular, less iron loss. To meet this requirement, it is important that secondary recrystallized grains are highly aligned in the steel sheet in the (110)[001] orientation (or the Goss orientation) and impurities in the product are reduced.
However, there are limitations on controlling crystal orientation and reduce impurities in terms of balancing with manufacturing cost, and so on. Therefore, some techniques have been developed for introducing non-uniformity to the surfaces of a steel sheet in a physical manner to reduce the magnetic domain width for less iron loss, namely, magnetic domain refining techniques. For example, JP 57-002252 B proposes a technique for reducing iron loss by irradiating a final product steel sheet with a laser, introducing a linear, high dislocation density region to the surface layer of the steel sheet and thereby reducing the magnetic domain width.
In addition, JP 06-072266 B proposes a technique for controlling the magnetic domain width by electron beam irradiation. In that method for reducing iron loss by electron beam irradiation, electron beam scanning can be performed at a high rate by controlling magnetic fields. In that method, there is no mechanically movable part as found in an optical scanning mechanism used in laser application. This is particularly advantageous when irradiating a series of wide strips, each having a width of 1 m or more, with an electron beam continuously at high rate.
However, even such a grain oriented electrical steel sheet that has been subjected to the magnetic domain refining treatment as described above may produce significant noise when assembled into an actual transformer.
It could therefore be helpful to provide a grain oriented electrical steel sheet with reduced iron loss by magnetic domain refinement treatment that exhibits excellent noise properties and may effectively reduce noise generated when used laminated on an iron core of a transformer.